There is many interesting books in SAP Press website, and you can also buy them in PDF version
I recommend you this 2:
1 - ABAP Objects
1 - ABAP to the Future
Besides this, look for an environment to test your codes. There is a German company that rent it, their name is IDE Acess. SAP has one free, but I didn't use that yet.
The other tip, try to check blogs. I have learnt a lot in them, and this is very nice.
The last tip? Check some ABAP resumes to know exactly what you must know to work in that area. Remembe, ABAP is a programming language, you're not a "consultant", you're a developer such as Java and .Net developers.
Good luck..!